High-quality crystal glasses have to meet the conditions for their use in terms of optical parameters, mechanical parameters and other physicochemical properties, as well as in terms of health and safety criteria. Due to the significant change in the assessment of the crystal glass after 1991, particularly in terms of their safety for health, environmental impact on the environment and toxicity to consumers, manufacturers are trying to modify properties of modern consumer and decorative glass so as to meet the above specified requirements. This can be achieved by changing the composition of the base glass matrix.
Currently, according to Directive 69/493/ECC four grades of crystal glass are produced, which grades are the highly leaded crystal, the leaded crystal, the crystaline and the crystal glass. However, by definition, all the glasses mentioned contain either lead oxide and/or barium oxide. The EU legislation, which is now in force, controls the use of compounds of the heavy metals such as Cd, Pb, Hg and Cr.
An example of such regulation is EU Directive No. 2002/95/ECC (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment—RoHS), issued Jan. 27, 2003 and amended Aug. 18, 2005 (which entered into force on Jul. 1, 2006). which Directive restricts the use of toxic metals in electrical and electronic equipment. This Directive restricts the use of these metals in light bulbs, electric discharge lamps, glass solders, but also in glass lighting accessories and consumer electronic items. Also, the EU Directive No. 94/62/ECC requires manufacturers to limit the harmful effects of heavy metals in the production and use of glass packaging containers.
Another limitation for the use of toxic metals represents The Consumer Product Safety Improvement Act—CPSIA, issued in 2008, dealing with the limits established by the Consumer Product Safety Commission—CPSC, which limits the products that are coming into contact with children under the age of 12 have to comply with. In Section 101, this Act stipulates that after Feb. 10, 2009, products designed or intended for children under 12 years must not contain more than 600 ppm of lead (leady ions), from Aug. 14, 2009, must contain less than 300 ppm of lead and starting with Aug. 14, 2011 limit can be reduced to 100 ppm and below. Artificial jewellery and ornamental objects are designed both for adults and children and the manufacturer must ensure the health safety and toxicological “safety” to all users.
For the leaded crystals characteristic are particularly their high density ≧2.9 g/cm3, high refractive index ≧1.545, and high optical dispersion. Technological properties are also favourable.
According to their density and refractive index, health safe glasses can be divided into two groups. The first group consists of glasses having density and refractive index that are comparable with those of the leaded crystal. These glasses are listed in Table 1 below. The other group consists of glasses having density, which is not according to the Directive 69/493/ECC and their refractive index is comparable with or lower than that of the leaded crystal. These glasses are listed in Table 2 and Table 3 below.
As it is shown in the tables, the following oxides: MgO, CaO, SrO, ZnO, La2O3, Bi2O3, TiO2, ZrO2, SnO2, Nb2O5, Ta2O5, Y2O3, Yb2O3 and WO3 were most commonly used in the glass skeleton as a substitute for PbO and BaO. All compounds used in the skeleton of the glass safe for health exhibit low toxicity or are non-toxic.
According to the patents granted on them, the compositions of the glasses listed in Table 1 contain neither the toxic PbO nor the BaO. The patent granted to the Baccarat company uses ZnO, SrO and CaO oxides as a replacement for PbO. The patent granted to the British Glass is based on the use of Bi2O3, TiO2 and SrO. The company Nachtmann stabilizes by a combination of TiO2, ZnO and SrO. The Swarovski company makes use preferably of a combination of the ZnO and CaO oxides. All the glasses mentioned are approaching the leaded crystal glass both in their density and their refractive index.
TABLE 1Composition of glasses having refractive index ≧1.54 anddensity>2.63 g/cm3Patent Owner/Patent No.BaccaratBritish GlassNachtmannSwarovskibOxideEP 0553586GB 2280432DE 10258923EP 1725502(wt. %)A1AA1A1SiO253-58  50-65  55-68 50-60Li2O0-0.3Σ M2O 12-23—0.5-3  Na2O4.5-7.5  5-1212-15K206-10 9-15<3MgO———<2CaO0-9  0-15a— 4-11SrO0-12 1-20 <5CaOreplacementBaO————ZnO16-21  0-15a3-10 8-16B2030-1.20-15a—0.6-4  Al2030-1.50-15a—0.25-5  La2030-3  0-15a—<5Bi203—1-20 —<3Ti020-2  1-15 8.5-14  <5Zr02—0-15a—<3Sn020-2.5——yesNb206———<1Ta205———<1Y203———<3Yb203———<1W03———<3ClarifyingSb, As, CeSb, As, CeSb, AsSbagentGuaranteed values of variablesρ[g/cm3]≧2.9≧2.7>2.63≧2.7nD≧1.545≧1.55≧1.54≧1.55aFurther, the glass contains by weight one oxide or more oxides from the group of the mentioned oxides at total level 15%,bBy weight, total amount of the Pb, Ba, As oxides is below 0.1%, total content of Ti and La oxides is below 5% and total content of Nb, Ta, Yb, Y, W, Bi, Zr oxides is below 5%, wherein it contains not more than 1% of each of the Nb, Ta, Yb oxides, and not more than 3% of each of the Y, W, Bi, Zr oxides. The total content by weight of ZnO and CaO is higher than 15%, CaO is partly replaced by SrO. The glass also contains 0.5-3% Li2O. Total content by weight of Na2O and Li2O is less than 17%. Total content by weight of other components, regardless of Sb2O3, Nd2O5 and Er2O3 is less than 2%.
According to the granted patents and the utility model, the glass compositions of the glass group, listed in Tables 2 and 3, also do not contain any toxic PbO or BaO.
TABLE 2Composition of glasses having refractive index ≧1.52 anddensity ≧2.43 g/cm3Patent Owner/Patent No.MoravskéInnsklárnyCrystal GlassMoserKv{hacek over (e)}tnáNachtmannOxideEP 0547263CZ 294797CZ 19984DE 19936699(wt. %)A1B6U1A1SiO265-7071.5-76.565.5-75.5  59-71Li2O——— 0.01-2Na2O 4-125-9 6-10   3-15K2O 4-12 8-12 8-12 0.08-11MgO——<2 0.5-8CaO6-95-95-9   2-10SrO——1-50.001-0.1BaO————ZnO4-70.5-3.5<4 0.01-11B2O30.5-5  0.5-3.5<2 0.01-3Al2O31-50.1-2.1<2 0.01-4La2O3——0.5-5.50.001-4Bi2O3————TiO21-6—— 0.01-8ZrO21-6———SnO2———0.001-3Nb2O5A———Ta2O5————Y2O3————Yb2O3————WO3————ClarifyingSbSbSbSb, As,agentSO42−, FGuaranteed values of variablesρ[g/cm3]>2.45>2.43>2.52>2.45nD≧1.52>1.52>1.52>1.52
The company Inn Crystal Glass discloses a glass based on CaO, ZnO, ZrO2 and/or TiO2 modifiers. The company Moser discloses glass based on the CaO and ZnO oxides. The utility model of the Moravské sklárny. Kv{hacek over (e)}tná, discloses glass based on a combination of CaO, MgO, SrO, ZnO and La2O3 oxides. Patent of the company Nachtmann discloses presence of CaO, MgO, ZnO, TiO2, La2O3 and SnO2 oxides and of a certain water content.
TABLE 3Composition of glasses having refractive index ≧1.52 anddensity ≧2.45 g/cm3Patent owner/Patent No.Toyo-sasakiFavrot, G. A.,RonaSchottaGlassTruyol, A.OxideSK 285523EP 0564802EP 2022767EP 0701976(wt. %)B6A1A1A1SiO265.1-71.950-7562-65  65-73Li2O—0-5—1.5-2.5Na2O 8-14 2-1510-12  4-8K2O6.5-9.9 5-158-10 0.2-0.7MgO<0.60-5—2-5CaO8.6-13  3-123-4.25-8SrO—0-72-3.2—BaO————ZnO0.5-3.60-76-7.21.2-3  B2O3— 0-10—5-8Al2O30.01-3  0-52-3.22.5-4  La2O3——0-1.2—Bi2O3————TiO2—0-82.2-3  0.3-0.8ZrO20.01-2.1 0-50-1.21.1-2.5SnO2——0-1.2—Nb2O5—0.1-5  ——Ta2O5—0-5——Y2O3——0-1.2—Yb2O3————WO3————ClarifyingSbSb, FSbCe, S042−agentGuaranteed values or variablesρ[g/cm3]≧2.45≧2.45≧2.6unspecifiednD≧1.52>1.52≧1.53unspecifiedaTotal content by weight of TiO2 + ZrO2 + Nb2O5 + Ta2U3 oxides is in the range 0.3-12%
The Slovak manufacturer of crystal glass, Rona, protects glass based on a high CaO content and the presence of ZnO, ZrO2, and MgO. The company Schott Glaswerke starts from an alkali-calcium skeleton, which is modified by a combination of the MgO, ZnO, TiO2, ZrO2, Nb2O5 and Ta2O5 oxides.
The company Toyo-Sasaki Glass provides glass with presence of the ZnO, CaO, SrO, TiO2, La2O3, SnO2 and Y2O3 oxides. And finally, inventors G. A. Favrot and A. Truyol disclose glass with the CaO, MgO, ZnO, ZrO2 and TiO2 oxides. This group of glass shows a lower value of glass density than what is that of the leaded crystal glass, and the refractive index also varies from lower values to the values comparable with those of the leaded crystal glasses.
Although the above mentioned lead-free glasses exhibit largely satisfactory properties, they still have these shortcomings. Some of them contain toxic As2O3 as clarifying agent, other ones use expensive and questionable components SrO, La2O3, Bi2O3, SnO2, Nb2O5, Ta2O5, Y2O3, Yb2O3, WO3, etc.
Another disadvantages of some of the solutions disclosed in the above-mentioned patent documents are high melting temperatures, relatively high content of the TiO2, ZrO2, B2O3 oxides, causing a yellowish hue of the resulting glass, respectively problems associated with volume and/or surface crystallization of glass. A high content of ZnO is often the cause of the increased corrosion of refractory materials used to build melting furnaces.
The objective of the invention is to eliminate these shortcomings.